Blind identification of an unknown interleaved convolutional code

We give here an efficient method to reconstruct the block interleaver and recover the convolutional code when several noisy interleaved codewords are given. We reconstruct the block interleaver without assumption on its structure. By running some experimental tests we show the efficiency of this method even with moderate noise

Blind recovery of k/n rate convolutional encoders in a noisy environment

http://jwcn.eurasipjournals.com/content/2011/1/168International audienceIn order to enhance the reliability of digital transmissions, error correcting codes are used in every digital communication system. To meet the new constraints of data rate or reliability, new coding schemes are currently being developed. Therefore, digital communication systems are in perpetual evolution and it is becoming very difficult to remain compatible with all standards used. A cognitive radio system seems to provide an interesting solution to this problem: the conception of an intelligent receiver able to adapt itself to a specific transmission context. This article presents a new algorithm dedicated to the blind recognition of convolutional encoders in the general k/n rate case. After a brief recall of convolutional code and dual code properties, a new iterative method dedicated to the blind estimation of convolutional encoders in a noisy context is developed. Finally, case studies are presented to illustrate the performances of our blind identification method

A Fast Method for Blind Identification of Punctured Convolutional Codes

The existing method for blind identification of a punctured convolutional code involves searching for dual words and the puncturing pattern exhaustively. As the length of the dual words and the code rate increase, the computational complexity of this method expands exponentially. To address this problem, a fast scheme for blind identification of punctured convolutional codes is proposed. First, a recursive algorithm for solving the parity check equation set is proposed. The dual word and generator polynomial bases of the punctured convolutional code are estimated by using the recursive algorithm. After this, by using the structural properties of the generator matrix of the blocked code, possible generator matrices of the punctured convolutional code are obtained. Finally, since a generator polynomial of the parent convolutional code can be recovered from any column of its polycyclic pseudocirculant matrix, the corresponding generator matrix of the parent code and the puncturing pattern are reconstructed simultaneously from an estimation of the generator matrix of the punctured code. The reconstructed generator matrix of the parent code with a minimal constraint length is determined to be the identification result. Simulation experiments show the effectiveness of the proposed method. As there is no need to search for the dual word and puncturing pattern exhaustively, the method can achieve fast identification of punctured convolutional codes. Additionally, the method is robust to bit errors in the received sequence

New Coding/Decoding Techniques for Wireless Communication Systems

Wireless communication encompasses cellular telephony systems (mobile communication), wireless sensor networks, satellite communication systems and many other applications. Studies relevant to wireless communication deal with maintaining reliable and efficient exchange of information between the transmitter and receiver over a wireless channel. The most practical approach to facilitate reliable communication is using channel coding. In this dissertation we propose novel coding and decoding approaches for practical wireless systems. These approaches include variable-rate convolutional encoder, modified turbo decoder for local content in Single-Frequency Networks, and blind encoder parameter estimation for turbo codes. On the other hand, energy efficiency is major performance issue in wireless sensor networks. In this dissertation, we propose a novel hexagonal-tessellation based clustering and cluster-head selection scheme to maximize the lifetime of a wireless sensor network. For each proposed approach, the system performance evaluation is also provided. In this dissertation the reliability performance is expressed in terms of bit-error-rate (BER), and the energy efficiency is expressed in terms of network lifetime

On the Tradeoff Between Accuracy and Complexity in Blind Detection of Polar Codes

Polar codes are a recent family of error-correcting codes with a number of desirable characteristics. Their disruptive nature is illustrated by their rapid adoption in the $5^{th}$-generation mobile-communication standard, where they are used to protect control messages. In this work, we describe a two-stage system tasked with identifying the location of control messages that consists of a detection and selection stage followed by a decoding one. The first stage spurs the need for polar-code detection algorithms with variable effort to balance complexity between the two stages. We illustrate this idea of variable effort for multiple detection algorithms aimed at the first stage. We propose three novel blind detection methods based on belief-propagation decoding inspired by early-stopping criteria. Then we show how their reliability improves with the number of decoding iterations to highlight the possible tradeoffs between accuracy and complexity. Additionally, we show similar tradeoffs for a detection method from previous work. In a setup where only one block encoded with the polar code of interest is present among many other blocks, our results notably show that, depending on the complexity budget, a variable number of undesirable blocks can be dismissed while achieving a missed-detection rate in line with the block-error rate of a complex decoding algorithm.Comment: 5 pages, 4 figures, fixes typo in Sect. IV-D; presented at the International Symposium on Turbo Codes & Iterative Information Processing (ISTC) 201

Overview of Turbo-Code Reconstruction Techniques

In this paper we analyze different techniques to blindly recover the parameters of turbo-code encoders with only the knowledge of noisy eavesdropped binary stream. We compare different strategies to reconstruct convolutional encoders, particularly when both are recursive systematic coders. We explain the intrinsic indetermination due to these techniques but also how to overcome such an issue in the case of turbo-code encoders. Moreover, we generalize Burel and al.\u27s particular reconstruction of the second (n,1)-encoder for (n,k)-encoders

Virheenkorjauskoodien tunnistus signaalitiedustelussa

Error correction coding is an integral part of a digital communication system. In signals intelligence the aim is to recover the transmitted messages and part of this task is identifying the used error correction coding method. The purpose of this study is to present a overview of different identification methods of forward error correcting codes and test the performance of these codes in a controlled setting. The codes that are discussed in this work are block codes and convolutional codes with a main focus on low density parity check (LDPC) codes and turbo codes. Test cases for LDPC code identification are presented and remarks about the performance and limits are made.Virheenkorjauskoodit ovat oleellinen osa digitaalista tietoliikennejärjestelmää. Signaalitiedustelussa tavoite on selvittää lähetetty viesti ja osa tätä tehtävää on käytetyn virheenkorjauskoodin selvittäminen. Tämän työn tarkoituksena on esittää yleiskatsaus erilaisiin virheenkorjaukoodien tunnistusmenetelmiin ja testata näiden menetelmien suorituskykyä kontroloiduissa olosuhteissa. Virheenkorjauskoodit, joita käsitellään tässä työssä ovat lohkokoodit ja konvoluutiokoodit ja pääpaino on low density parity check (LDPC) -koodeissa ja turbokoodeissa. LDPC-koodin tunnistamismenetelmien testitulokset esitetään ja menetelmien suorituskykyä ja rajoitteita tarkastellaan

Contribution to the construction of fingerprinting and watermarking schemes to protect mobile agents and multimedia content

The main characteristic of fingerprinting codes is the need of high error-correction capacity due to the fact that they are designed to avoid collusion attacks which will damage many symbols from the codewords. Moreover, the use of fingerprinting schemes depends on the watermarking system that is used to embed the codeword into the content and how it honors the marking assumption. In this sense, even though fingerprinting codes were mainly used to protect multimedia content, using them on software protection systems seems an option to be considered. This thesis, studies how to use codes which have iterative-decoding algorithms, mainly turbo-codes, to solve the fingerprinting problem. Initially, it studies the effectiveness of current approaches based on concatenating tradicioanal fingerprinting schemes with convolutional codes and turbo-codes. It is shown that these kind of constructions ends up generating a high number of false positives. Even though this thesis contains some proposals to improve these schemes, the direct use of turbo-codes without using any concatenation with a fingerprinting code as inner code has also been considered. It is shown that the performance of turbo-codes using the appropiate constituent codes is a valid alternative for environments with hundreds of users and 2 or 3 traitors. As constituent codes, we have chosen low-rate convolutional codes with maximum free distance. As for how to use fingerprinting codes with watermarking schemes, we have studied the option of using watermarking systems based on informed coding and informed embedding. It has been discovered that, due to different encodings available for the same symbol, its applicability to embed fingerprints is very limited. On this sense, some modifications to these systems have been proposed in order to properly adapt them to fingerprinting applications. Moreover the behavior and impact over a video produced as a collusion of 2 users by the YouTube’s s ervice has been s tudied. We have also studied the optimal parameters for viable tracking of users who have used YouTube and conspired to redistribute copies generated by a collusion attack. Finally, we have studied how to implement fingerprinting schemes and software watermarking to fix the problem of malicious hosts on mobile agents platforms. In this regard, four different alternatives have been proposed to protect the agent depending on whether you want only detect the attack or avoid it in real time. Two of these proposals are focused on the protection of intrusion detection systems based on mobile agents. Moreover, each of these solutions has several implications in terms of infrastructure and complexity.Els codis fingerprinting es caracteritzen per proveir una alta capacitat correctora ja que han de fer front a atacs de confabulació que malmetran una part important dels símbols de la paraula codi. D'atra banda, la utilització de codis de fingerprinting en entorns reals està subjecta a que l'esquema de watermarking que gestiona la incrustació sigui respectuosa amb la marking assumption. De la mateixa manera, tot i que el fingerprinting neix de la protecció de contingut multimèdia, utilitzar-lo en la protecció de software comença a ser una aplicació a avaluar. En aquesta tesi s'ha estudiat com aplicar codis amb des codificació iterativa, concretament turbo-codis, al problema del rastreig de traïdors en el context del fingerprinting digital. Inicialment s'ha qüestionat l'eficàcia dels enfocaments actuals en la utilització de codis convolucionals i turbo-codis que plantegen concatenacions amb esquemes habituals de fingerprinting. S'ha demostrat que aquest tipus de concatenacions portaven, de forma implícita, a una elevada probabilitat d'inculpar un usuari innocent. Tot i que s'han proposat algunes millores sobre aquests esquemes , finalment s'ha plantejat l'ús de turbocodis directament, evitant així la concatenació amb altres esquemes de fingerprinting. S'ha demostrat que, si s'utilitzen els codis constituents apropiats, el rendiment del turbo-descodificador és suficient per a ser una alternativa aplicable en entorns amb varis centenars d'usuaris i 2 o 3 confabuladors . Com a codis constituents s'ha optat pels codis convolucionals de baix ràtio amb distància lliure màxima. Pel que fa a com utilitzar els codis de fingerprinting amb esquemes de watermarking, s'ha estudiat l'opció d'utilitzar sistemes de watermarking basats en la codificació i la incrustació informada. S'ha comprovat que, degut a la múltiple codificació del mateix símbol, la seva aplicabilitat per incrustar fingerprints és molt limitada. En aquest sentit s'ha plantejat algunes modificacions d'aquests sistemes per tal d'adaptar-los correctament a aplicacions de fingerprinting. D'altra banda s'ha avaluat el comportament i l'impacte que el servei de YouTube produeix sobre un vídeo amb un fingerprint incrustat. A més , s'ha estudiat els paràmetres òptims per a fer viable el rastreig d'usuaris que han confabulat i han utilitzat YouTube per a redistribuir la copia fruït de la seva confabulació. Finalment, s'ha estudiat com aplicar els esquemes de fingerprinting i watermarking de software per solucionar el problema de l'amfitrió maliciós en agents mòbils . En aquest sentit s'han proposat quatre alternatives diferents per a protegir l'agent en funció de si és vol només detectar l'atac o evitar-lo en temps real. Dues d'aquestes propostes es centren en la protecció de sistemes de detecció d'intrusions basats en agents mòbils. Cadascuna de les solucions té diverses implicacions a nivell d'infrastructura i de complexitat.Postprint (published version